Method for manufacturing battery pack

ABSTRACT

A heat insulation sheet ( 16 ) covers a temperature fuse ( 10 ) arranged on a sealing plate ( 23 ) of a rechargeable battery ( 2 ) so as to provide a shield from heat of resin that is filled in a gap between the rechargeable battery ( 2 ) and a circuit substrate ( 3 ) to form a primary mold ( 11 ) and to prevent destruction of the temperature fuse ( 10 ) caused by the heat.

TECHNICAL FIELD

The present invention relates to a battery pack in which constituentelements are united by filling with resin to reduce size and improverigidity so that it is suitable as a power source for portableelectronic equipment, and a manufacturing method thereof.

BACKGROUND ART

With the remarkable development of small, thin, and high-functionalityportable electronic equipment such as mobile phones and PDAs, there is agrowing demand for smaller, thinner, and high-capacity batteries astheir power source. Lithium ion rechargeable batteries can be designedsmall and high-capacity, and in particular, flat prismatic types aresuitable in making the equipment thinner; they have therefore beenincreasingly used as the repeatedly usable rechargeable battery forportable electronic equipment.

Because lithium ion rechargeable batteries have high energy density andcontain a flammable organic solvent as electrolyte, it is essential totake account of safety measures. They must have such safety features asto ensure that no damage is caused to the equipment or injury to theuser in the event that an abnormality arises for some reason. Forexample, if the positive and negative terminals of the battery areshort-circuited for some reason, a large short-circuit current flows inhigh energy density batteries, whereupon the inner resistance generatesJoule heat and the battery temperature rises. A temperature rise in thebattery leads to a rapid increasing of inner gas pressure caused byreactions between positive electrode active materials and electrolyte,or from evaporation or decomposition of electrolyte, which results infire or explosion of the battery. Batteries may fall into ahigh-temperature state not only because of external short-circuiting butalso of overcharge; the same applies if the portable electronicequipment loaded with the battery is placed near a heater or left insidea car parked in a hot weather environment.

A battery abnormality can be induced by any of electrical, mechanical,or thermal factors; thus non-aqueous electrolyte batteries representedby lithium ion rechargeable batteries are provided with safety featuresfor preventing batteries from falling into an abnormal state and forevading a further dangerous state even if an abnormality should arise.Such features are usually incorporated in batteries as their ownnatures; for example, active materials on the electrodes and electrolytemay be made not to be excessively reactive, or, a polyolefin porous filmmay be employed for the separator because of its “shutdown function,” inwhich minute pores are softened and close under an abnormally hightemperature. Cylindrical lithium ion rechargeable batteries are usuallyprovided with a protective feature such as a Positive TemperatureCoefficient (PTC) element connected in series to the input/outputcircuit at the sealing end, which limits current flow in the event ofexternal short-circuiting. Batteries that do not have a sufficient spacefor the PTC element inside are normally provided with a PTC element ortemperature fuse as outside circuit components. Further, a circuit forprotecting the battery from overcharge and over discharge is an absoluterequirement. In general, these constituent elements are all packed withthe battery inside a pack case to form a battery pack.

However, battery packs using pack cases are not suited to portableelectronic equipment that are re-modeled in short cycles, because themanufacturing cost of molding dies used in the resin molding of packcases tends to be high, and the time required for designing new moldingdies is relatively long. Battery packs with resin-molded outer casesalso have limitations in making portable electronic equipment smallerand thinner because of the limitations on the moldable thickness in theresin molding process.

Furthermore, in order to prevent the user from disassembling a batterypack for wrong use or for satisfying curiosity, it must have a designthat is hardly disassemblable, or a design that alerts the user that ithas been disassembled.

Taking account that the battery packs are used for portable electronicequipment, they also need to have a rigid structure that can withstandvibration or shocks in a falling accident, and a moisture resistance,particularly for the electronic circuit parts. In achieving thestructure having a disassemblablity, a certain rigidity, and a moistureresistant, the idea has emerged that a battery may be united with acircuit substrate including a battery protective circuit by resinmolding.

Such resin-molded battery packs described above are disclosed inJapanese Laid-Open Patent Publications Nos. 2002-134077 and 2002-166447,in which a battery and a circuit substrate are connected by a connectingmember to form an intermediate product, which is placed inside a die,and resin is filled around the intermediate product such as to exposeexternal terminals formed on the circuit substrate to the outside.

Japanese Laid-Open Patent Publication No. 2000-315483 discloses astructure in which a battery and a circuit substrate are connected by aconnecting member and placed inside a die, and the circuit substrate isresin-sealed and fixed on the battery or its pack case (battery lid), orboth the circuit substrate and the battery are resin-sealed.

Battery packs of lithium ion rechargeable batteries are normallyprovided with a battery protection feature that prevents a temperaturerise caused by external short-circuiting or overcharge as mentionedabove, and in addition, they are provided with a heat sensitive elementsuch as a temperature fuse or PTC element that cuts the battery circuitas a backup safety feature in the event that the protective feature hasnot functioned.

Because the heat sensitive element is heat-coupled to the rechargeablebattery so that it operates not only in an over current condition butalso upon a change in the battery temperature, and connected to thecircuit that connects the rechargeable battery with the circuitsubstrate, a measure must be taken so that the heat sensitive element isnot destroyed by the heat of the resin filled between the rechargeablebattery and the circuit substrate during the resin molding. Generally,temperature fuses have a fusion temperature of 104° C.; on the otherhand, the temperature of molten resin, even though it is a hot meltresin that melts at a relatively low temperature, exceeds 200° C. Whilehot melt resins have a lower melting temperature than other moldingresins and allow easy handling, the melting temperature is still muchhigher than the fusion temperature of the temperature fuse. A directcontact of molten hot melt resin with the temperature fuse willcertainly induce fusion, whereby the circuit in the battery pack will becut and not properly function. In the case with a PTC element, hot resinof more than 200° C. will change the bridging structure of theconductive polymer that is a chief component of the PTC element, wherebythe temperature-current characteristics and trip temperature will beaffected and the reliability of the PTC element will be deteriorated.Accordingly, in the production of battery packs of a rechargeablebattery and a circuit substrate united by filling with resin with safetyfeatures using heat sensitive elements, it is an absolute requirement toprovide measures to prevent destruction of the heat sensitive elements.

It is an object of the invention to provide a battery pack of a batteryand a circuit substrate that are united by resin molding, the batterypack having a structure that prevents a heat sensitive element providedas a safety feature from being destroyed by filled resin, and amanufacturing method thereof.

DISCLOSURE OF THE INVENTION

To achieve the above object, a battery pack according to a first aspectof the present invention comprises a substrate formed with an externalterminal that is arranged on a sealing plate side of a rechargeablebattery with a gap therebetween and united with the rechargeable batteryby resin filled in that gap; and a heat sensitive element heat-coupledto the rechargeable battery that is arranged in the gap and providedwith a heat shield by constituent elements of the battery pack exceptfor the molded resin. The constituent elements other than the resin suchas connection leads and insulation sheets are arranged to surround theheat sensitive element so that they provide a shield from heat of theresin when molten or softened resin of high temperature is filled in thegap, whereby a direct contact of the high-temperature resin with theheat sensitive element is avoided, and destruction or deterioration ofthe functions and characteristics of the heat sensitive element isprevented. Moreover, because the heat sensitive element is heat-coupledto the rechargeable battery, the precision in sensing the rechargeablebattery temperature is high. This feature is characteristic of theinvention, i.e., even with the characteristic structure of the batterypack of the invention in which the heat sensitive element is arranged inthe gap between the rechargeable battery and the substrate and resin isfilled between in this gap, an improvement is made in the precision insensing the battery temperature. The heat-coupling is achieved by adirect contact between the rechargeable battery and the heat sensitiveelement so that the heat sensitive element senses the heat of therechargeable battery and detects its temperature with high precision.Alternatively, the heat-coupling may be achieved by a heat conductive,insulating material such as silicon resin interposed between therechargeable battery and the heat sensitive element. Insulation isthereby provided between the rechargeable battery and the heat sensitiveelement. It is also preferable in terms of sensing precision because theheat conductivity will be much better than by simply making contact.

A battery pack according to a second aspect of the present inventioncomprises a substrate formed with an external terminal that is arrangedopposite a rechargeable battery with a gap therebetween and united withthe rechargeable battery by resin filled in that gap; and a heatsensitive element heat-coupled to the rechargeable battery that isarranged in the gap and covered by a heat insulation member. Because theheat sensitive element is covered by the heat insulation member, resindoes not contact the heat sensitive element directly when it is filledbetween the rechargeable battery and the circuit substrate and flowsonto the heat sensitive element. Since heat conduction from the resin tothe heat sensitive element is suppressed by the heat insulation member,destruction of the heat sensitive element during the resin molding inthe process of forming the battery pack is prevented. The heatinsulation member is typically a sheet of known heat insulatingmaterials such as resins and inorganic substances; it should provide aheat shield for the heat sensitive element, as well as have insulationrelative to the constituent elements such as connection leads and thelike arranged in the gap. The heat sensitive element may be covered by aheat insulating resin material instead of providing the heat insulationsheet. Either way, the heat sensitive element is electrically connectedto one of the positive and negative electrodes of the rechargeablebattery, heat-coupled to the rechargeable battery, and set in apredetermined position. After that, the heat sensitive element iscovered by the heat insulation member by a process of arranging the heatinsulation sheet to cover the heat sensitive element, or, covering theheat sensitive element by a resin material.

A battery pack according to a third aspect of the present inventioncomprises a substrate formed with an external terminal that is arrangedon a sealing plate side of a rechargeable battery with a gaptherebetween and united with the rechargeable battery by resin filled inthat gap; and a heat sensitive element heat-coupled to the rechargeablebattery that is arranged in a recess formed in the sealing plate andprovided with a heat insulation member or other constituent elementscovering the recess. Because the heat sensitive element is arranged inthe recess that is covered by other constituent elements, the filledresin does not contact the heat sensitive element, and the battery packis formed without the risk of destroying the heat sensitive element withthe heat of molten resin during the resin filling. Further, heat of therechargeable battery is well conducted to the heat sensitive elementbecause it is arranged in the recess, and it operates swiftly inresponse to an abnormal temperature rise in the rechargeable battery.

A battery pack according to a fourth aspect of the present inventioncomprises a substrate formed with an external terminal that is arrangedon a sealing plate side of a rechargeable battery with a gaptherebetween and united with the rechargeable battery by resin filled inthat gap; and a heat sensitive element heat-coupled to the rechargeablebattery that is arranged in the gap and formed with a heat insulationcoating layer. The coating layer on the heat sensitive element has heatinsulating properties, and a direct contact of the element with thehigh-temperature molten resin is avoided by arranging this side with thecoating layer to contact the molten resin, whereby deterioration of itscharacteristics is prevented. With this structure, because the heatsensitive element is protected by the coating layer, there is no need ofcovering the element with a heat insulation member. By the eliminationof the heat insulation means, the number of process steps and componentsin the production are reduced, whereby a cost reduction is achieved. Thecoating layer should preferably be made of a resin material having heatinsulating properties. Further, the heat sensitive element shouldinclude a portion that is not provided with the coating layer so that itis contacted and heat-coupled to the rechargeable battery in thatportion. Thus coating layer is not formed in the portion that is incontact with the rechargeable battery, whereby the heat sensitiveelement has both a heat shield during the resin molding and high sensingprecision of the rechargeable battery temperature. In order to preventan increase in the process steps and complication in the process ofarranging the heat sensitive element on the rechargeable battery, asuitable resin material should be selected; it should be able to providethe heat shield effect during the short period of resin molding, andhave thermal characteristics that do not cause a decrease in the sensingprecision of the rechargeable battery temperature after the battery packis complete. Thereby, the heat sensitive element has the heat shield andhigh sensing precision, and is provided with fewer process steps and atlower cost.

In any of the above structures, the heat sensitive element is typicallya temperature fuse, which fuses and thereby cuts the battery circuitupon an abnormal temperature rise in the rechargeable battery, thusterminating the connection with the battery circuit that is causing thetemperature rise. The heat sensitive element may also be a PTC element,which limits current flow in the event of external short-circuiting andstops current flow in the battery circuit by increasing resistance inresponse to an abnormal temperature rise in the rechargeable battery,thus terminating the connection with the battery circuit that is causingthe temperature rise. The heat sensitive element may also be a bimetalthermostat, which cuts current flow upon a temperature rise in the eventof external short-circuiting and limits current flow in the batterycircuit by cutting the circuit in response to an abnormal temperaturerise in the rechargeable battery, thus terminating the connection withthe battery circuit that is causing the temperature rise.

A method for manufacturing a battery pack according to a fifth aspect ofthe present invention comprises: arranging a substrate formed with anexternal terminal that is connected to a rechargeable battery, oppositethe rechargeable battery with a gap therebetween for forming an objectto be resin packed, which is placed inside a die; and filling the gapwith resin for uniting the rechargeable battery and the substrate,wherein the die in which the object to be resin packed is placed andresin is filled in the gap is formed of a material having good heatconductivity at least in a portion corresponding to the position where aheat sensitive element arranged inside the gap is located. By formingthe die from a material having good heat conductivity in the portioncorresponding to the position of the heat sensitive element, heat of thefilled resin conducts well to that portion made of the heat conductivematerial, whereby heat conduction from the resin to the heat sensitiveelement is reduced. The battery pack of the rechargeable battery unitedwith the substrate by resin molding is thus produced without the risk ofdestroying the heat sensitive element by the heat of the filled resin.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating an external appearance of abattery pack according to one embodiment of the invention;

FIG. 2 is an exploded perspective view illustrating various constituentelements of the above battery pack;

FIG. 3A is a plan view illustrating the structure of a rechargeablebattery, FIG. 3B is a cross section of the rechargeable battery on theside of a sealing plate, and FIG. 3C is a plan view illustrating therechargeable battery to which a temperature fuse is attached;

FIG. 4A is a perspective view illustrating the structure of a circuitsubstrate on the outer side, FIG. 4B is a perspective view illustratingthe structure of the circuit substrate on the inner side, and FIG. 4C isa perspective view illustrating the circuit substrate to which a leadplate is attached;

FIG. 5A and FIG. 5B are perspective views illustrating how the circuitsubstrate is attached to the rechargeable battery;

FIG. 6 is a schematic view for explaining how positioning is achieved bya molding die;

FIG. 7 is a perspective view illustrating the structure of a primarymolding die;

FIG. 8 is a cross-sectional view illustrating a resin mold formed by theprimary molding;

FIG. 9 is a perspective view illustrating the structure of a secondarymolding die;

FIG. 10 is a cross-sectional view illustrating a resin mold formed bythe secondary molding;

FIG. 11A to FIG. 11C are perspective views illustrating a formationprocess of production steps in chronological order;

FIG. 12 is a cross-sectional view for explaining where a connecting partis formed; and

FIG. 13 is a cross-sectional view illustrating an alternative structurefor installing a temperature fuse.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will be hereinafterdescribed with reference to the accompanying drawings for anunderstanding of the invention. It should be understood that thefollowing embodiments of the invention are merely given as examples andshould not limit the technical scope of the invention.

The present embodiment shows one example of a battery pack employing aflat prismatic lithium ion rechargeable battery applied to a mobilephone. Battery packs for mobile phones need to be small, light-weight,and thin, and in addition, they are desired to have a high energydensity in accordance with high functionality, a high mechanicalstrength to withstand impacts caused by a falling accident which isinevitable with portable equipment, a structure that does not allow easydisassembling, and safety features for protecting the rechargeablebattery from short circuits, overcharge, and high temperature. Thebattery pack described below satisfies all these requirements.

FIG. 1 is an outer representation of the battery pack 1 according tothis embodiment. On one end face of the flat battery pack are exposedexternal terminals 6 consisting of a positive terminal, a negativeterminal, and a temperature detecting terminal, and bonded a wateringress label 9. FIG. 2 is an exploded view of this battery pack 1showing its constituent elements. These elements and a manufacturingmethod of the battery pack 1 will be described below in detail.

The lithium ion rechargeable battery (hereinafter rechargeable battery)2 accommodates elements for electromotive force in a bottomed tube-likealuminum case 22 having an oval cross section as can be seen from FIGS.3A to 3B, the open end of the case 22 being sealed with a sealing plate23 by laser welding. The sealing plate 23 is joined to the case 22 andserves as the battery's positive electrode; the battery's negativeelectrode 25 is electrically insulated from the sealing plate 23 by anupper gasket 24 a and a lower gasket 24 b and protruded at the center ofthe sealing plate 23. On both sides of the sealing plate 23 aremushroom-shaped engaging protrusions 26, 26 that are provided bypress-forming. Reference numeral 27 denotes a plug for closing a holefor pouring electrolyte; after the injection of electrolyte into thecase 22, the hole is closed by the plug 27, which is then welded to thesealing plate 23.

The engaging protrusions 26 are formed into the mushroom shape as shownby first pressing the sealing plate 23 to provide cylindricalprojections at preset locations on the sealing plate 23 and spreadingthe tops of the projections by pressing. Pressing is not the only way toform the engaging protrusions 26; they may be formed by weldingmushroom-shaped or inverted L shape members onto the sealing plate 23,as will be described later.

To the negative electrode 25 of this rechargeable battery 2 isspot-welded a connection piece 10 a at one end of a temperature fuse(heat sensitive element) 10 as shown in FIG. 3C. A heat insulation sheet16 is affixed upon the upper face of the temperature fuse 10 asindicated by broken lines, so as to prevent fusion of the temperaturefuse 10 during the resin filling process to be described later. The heatinsulation sheet 16 used here is a 0.6 mm thick acrylic foam sheet (VHB:Sumitomo 3M Ltd.) consisting of a foamed acrylic resin sheet providedwith an adhesive layer, but other materials may also be used as will bedescribed later. A connection piece 10 b at the other end of thetemperature fuse 10 is placed upon an insulating paper 21 affixed on thesealing plate 23 and connected to a negative lead plate 5 to bedescribed later. The temperature fuse 10 is fixed on the sealing plate23 by heat conductive adhesive so as to be heat-coupled to therechargeable battery 2.

The circuit substrate 3 includes a circuit for protecting therechargeable battery 2 from overcharge, over discharge, and overcurrent; on one side that is on the outside are formed theaforementioned external terminals 6 and the test terminal 30 as shown inFIG. 4A, and on the other side that is on the side of the rechargeablebattery 2 are mounted electronic components 31 such as ICs and positiveand negative solder lands 32, 33 at both ends for the connection withthe rechargeable battery 2, as shown in FIG. 4B. Incidentally, circuitpatterns and through holes on the circuit board 3 are not shown in thesedrawings. one end of a positive lead plate (connecting member) 4 issoldered to the positive solder land 32, with a piece of insulatingpaper 34 interposed between the lead plate 4 and the electroniccomponents 31, and one end of the negative lead plate (connectingmember) 5 is soldered to the negative solder land 33.

After establishing these connections, the circuit substrate 3 is setrelative to the rechargeable battery 2 as shown in FIG. 5A such that theother end of the positive lead plate 32 is spot-welded on the face ofthe sealing plate 23, and the other end of the negative lead plate 33 onthe connection piece 10 b of the temperature fuse 10. The circuitsubstrate 3 is orthogonal to the face of the sealing plate 23 in thisconnection state; the positive and negative lead plates 4, 5 are thenbent over so that the circuit substrate 3 is substantially parallel tothe sealing plate 23 with a certain gap therebetween, as shown in FIG.5B. The rechargeable battery 2 with the circuit substrate 3 thusconnected thereto constitutes an object 7 to be resin packed shown inFIG. 11A.

Resin is filled between the rechargeable battery 2 and the circuitsubstrate 3 of the object 7 to be resin packed to integrate them. It isimportant to ensure that the height H from the bottom face of therechargeable battery 2 to the surface of the circuit substrate 3 wherethe external terminals 6 are formed is precisely controlled in the resinmolding process; the following is a description of a manufacturingmethod in which this is achieved.

As shown in FIG. 6, a lower die 36 of the primary molding die 35includes a movable part 41 that is movable towards a stationary part 42by biasing means 45, and the movable part 41 is provided with a vacuumsuction part 43. The object 7 to be resin packed (only the rechargeablebattery 2 and the circuit substrate 3 being illustrated in the drawing)is placed inside the lower die 36 with the movable part 41 retracted,which is then moved forward for the positioning of the rechargeablebattery 2, with its bottom being pressed against the inner wall of thestationary part 42. The circuit substrate 3, on the other hand, makestight contact with the wall of the vacuum suction part 43 and is kept inposition.

The height H from the bottom face of the rechargeable battery 2 to thesurface of the circuit substrate 3 where the external terminals 6 areformed varies because of variations in the height h of the rechargeablebattery 2 and in the position of the circuit substrate 3; with the abovestructure, however, the circuit substrate 3 is fixed in position byvacuum suction, while the movable part 41 changes its position inaccordance with the height h of the rechargeable battery 2, so that theclearance G between the rechargeable battery 2 and the circuit substrate3 placed inside the lower die 36 is variable, whereby the height H fromthe bottom face of the rechargeable battery 2 to the surface of thecircuit substrate 3 where the external terminals 6 are formed is madeconstant.

An upper die 37 shown in FIG. 7 is lowered onto the lower die 36 inwhich the rechargeable battery 2 and the circuit substrate 3 are placedin position, and resin is injected from a gate 44 in the upper die 37into the gap between the rechargeable battery 2 and the circuitsubstrate 3. The injected resin surrounds the electronic components 31and positive and negative lead plates 4, 5 on the circuit substrate 3and bonds to the circuit substrate 3, as well as surrounds the undercutportions of the engaging protrusions 26 on the sealing plate 23 of therechargeable battery 2 and bonds to the sealing plate 23, as shown inFIG. 8. Hot melt resins are preferably used because they melt at atemperature that does not adversely affect the electronic components 31,battery 2, and temperature fuse 10, and cure as the temperature lowers.

Even though the resin melts at a relatively low temperature, it is stillas hot as 200° C.; if it contacts the temperature fuse 10 whose fusiontemperature is set 104° C., it may cause fusion of the fuse and destroythe function of the battery pack 1. As a countermeasure, the heatinsulation sheet 16 is affixed to cover the temperature fuse 10 asmentioned above so as to provide a shield from heat of resin for thetemperature fuse 10.

After curing the filled resin, the upper die 37 is opened, vacuumsuction by the vacuum suction part 43 stopped, and the movable part 41retracted, an intermediate product 8 shown in FIG. 11B, which consistsof the rechargeable battery 2 and the circuit substrate 3 united by aprimary mold 11 that is formed by the cured resin, is taken out from thelower mold 36. This intermediate product 8 is made into a battery pack 1by providing an outer covering.

The outer covering is provided by a secondary molding process and awinding sheet affixing process. An insulator 14 is attached to thebottom face of the rechargeable battery 2 before the secondary molding.

In the secondary molding, the intermediate product 8 is placed in asecondary molding die 46 shown in FIG. 9, so that predetermined parts ofthe intermediate product 8 are packed with resin. A lower die 47 of thesecondary molding die 46 has a cavity 50 for accommodating theintermediate product 8; in a wall on one side of the cavity 50 areprovided inwardly biased projections 51, 52 for the three externalterminals and test terminal, and in the opposite wall is provided aninwardly biased projection 54 for the bottom face of the battery. Whenthe intermediate product 8 is placed in the cavity 50 and theseprojections 51, 52, 54 are moved forward, the projections 51 makepressure contact with the external terminals 6 at three locations on thecircuit substrate 3, and the projection 54 with the insulator 14 bondedon the bottom face of the rechargeable battery 2, respectively.

The lower die 47 in this state is then closed by an upper die 48, andresin is filled from a gate 53 in the upper die 48 into the secondarymolding die 46. The resin is injected into the die 46 from fourlocations for forming the following: An upper mold 17 fixed on thesealing plate 23 of the rechargeable battery 2 as shown in FIG. 11C andcovering the circuit substrate 3 and the primary mold 11 while exposingthe external terminals 6 and the test terminal 30 of the intermediateproduct 8 to the outside as shown in FIG. 10; a lower mold 18 fixed onthe bottom face of the rechargeable battery 2 to a predeterminedthickness such as to surround the insulator 14; and a connecting part 19for coupling the upper mold 17 and the lower mold 18 along two cornerson one side of the rechargeable battery. The connecting part 19 isformed such that the two parts of the arc on one side of the oval crosssection of the rechargeable battery 2 at 90 degrees are right-angled, asshown in FIG. 12. The upper mold 17, the lower mold 18, and theconnecting part 19 together form the secondary mold 12 shown in FIG. 2.

The upper mold 17 has a step 38 in its periphery near the rechargeablebattery, which defines a positioning line along which a winding sheet 13is wound around the periphery of the rechargeable battery 2. The batteryoperation is then inspected using the test terminal 30, and the wateringress label 9 is bonded in the cavity surrounding the test terminal 30of the batteries that have passed the inspection to cover the testterminal 30, whereby the battery pack 1 shown in FIG. 1 is obtained.

The battery pack 1 thus formed has curved shoulders on one flat sidecorresponding to the arc on both sides of the rechargeable battery 2,while the other two corners on the opposite side are right-angledbecause of the connecting part 19; this feature, coupled with theasymmetric arrangement of the external terminals 6, prevents the batteryto be reversely loaded in equipment. The curved corners will snugly fitin rounded corners in the battery accommodation case of the equipmentwithout leaving any dead space.

In the above structure, the heat insulation sheet 16 is affixed toprevent destruction or degeneration of the heat sensitive element suchas the temperature fuse 10 because of the heat of molded resin; anotherpossibility is to means for reducing thermal effects of molten resin onthe heat sensitive element during the period in which the resin cures.Such heat insulation may be achieved either by affixing a heatinsulation sheet on the heat sensitive element, or by covering the heatsensitive element with resin having heat insulating properties.

Heat insulating resins that are preferably used for covering the heatsensitive element should have a higher melting temperature than that ofthe filled resin, and include polyphenylene sulfide (PPS), polyamide(PA), polyamideimide (PAI), polyimide (PI), and polyetheretherketone(PEEK). More preferably, the heat insulating resin should have a goodbond with the filled resin.

The heat insulation sheet affixed on the heat sensitive element may be afoamed acrylic resin or polyurethane sheet, or a sheet made of the aboveheat insulating resins, polyurethane, liquid crystal polymers, phenolicresins, or fluorine resins. Alternatively, a ceramic, glass wool, orglass cloth sheet impregnated with heat resistant resin may also beemployed. These sheets should preferably have a thickness of about 0.3to 1.0 mm for the purposes of heat insulation from molten resin andprotection from injection pressure.

Other countermeasures to prevent thermal effects of resin on thetemperature fuse 10 when molding resin between the rechargeable battery2 and the circuit substrate 3 include the following structure or moldingmethod.

As shown in FIG. 13, a recess 28 is formed in the sealing plate 23 ofthe battery 2, and the temperature fuse 10 is placed inside this recess28. A heat insulation sheet 16 may be affixed above the temperature fuse10 such as to close the open top of the recess 28, or other constituentelements may be employed for stopping resin from flowing into the recess28, to achieve the same effect. With the latter structure, the heat ofthe rechargeable battery 2 conducts to the temperature fuse 10 better,i.e., the temperature fuse 10 detects an abnormal temperature rise inthe rechargeable battery 2 with higher precision and response speed. Theconnection pieces 10 a, 10 b at both ends of the temperature fuse 10 areinsulated from the sealing plate 23 respectively by the insulating paper29, 29, while the body of the temperature fuse 10 is fixed inside therecess 28 with a heat conductive adhesive (e.g. silicon resin) andheat-coupled to the rechargeable battery 2.

A portion of the primary molding die 35 where the temperature fuse 10will be located may be formed of a material having good heatconductivity (e.g. aluminum) so as to diffuse heat from the resin intothe die and reduce heat conduction to the temperature fuse 10, wherebyfusion of the temperature fuse 10 during the resin molding is prevented.

Alternatively, the entire primary molding die 35, or at least thestationary part 42 of its lower die 36 may be formed of a materialhaving good heat conductivity (e.g. aluminum alloy) so as to enhanceheat conductivity of the portion where the temperature fuse 10 will belocated.

Further, both the primary and secondary molding dies 35, 46 are formedwith an insulating layer in the parts where active parts of the object 7to be resin packed or the intermediate product 8 such as positive andnegative lead plates 4, 5, external terminals 6 and test terminal 30will be located, so as to prevent short circuits or leaks caused by acontact between the active parts and molding dies. The insulating layershould preferably be formed on the aluminum molding dies by alumiteprocessing or fluorine resin coating processing so that the dies willhave insulation as well as excellent heat conductivity.

The heat insulation sheet is provided as a shield from heat of moldingresin for the temperature fuse in the above-described structure, but aconnection lead for electrically connecting the rechargeable batterywith the substrate may be used instead of the heat insulation sheet tocover the temperature fuse so as to shield it from the heat of themolding resin.

The temperature fuse 10 in the above-described structure may be replacedby a PTC element. As well known, a PTC element functions by increasingits normally small resistance in response to a temperature rise to apreset value to stop current flow. When a large current flows because ofa short circuit, for example, the PTC element generates heat to increaseresistance to limit the current flow. If heat-coupled to therechargeable battery 2, it increases resistance in response to anabnormal temperature rise in the rechargeable battery 2 toinstantaneously limit the current flow that is causing the temperaturerise and stops the temperature rise.

A direct contact of molten resin during the molding with the PTC elementmay destroy its function. Accordingly, a heat shield structure should beprovided similarly to the case with the temperature fuse 10.

Also, the temperature fuse 10 in the above-described structure may bereplaced by a bimetal thermostat. A bimetal thermostat has a movablecontact formed by two types of metal that have different thermalexpansion coefficients, and functions to stop current flow by openingthe movable contact in response to a temperature rise to a preset valueby deformation caused by the difference in the thermal expansioncoefficient. When a large current flows because of a short circuit, forexample, it generates heat and raises temperature to stop the currentflow. If heat-coupled to the rechargeable battery 2, it senses anabnormal temperature rise in the rechargeable battery 2 and cuts thecurrent flow that is causing the temperature rise to stop thetemperature rise.

A direct contact of filled resin during the molding with the bimetalthermostat may adversely affect its function due to heat shock.Accordingly, a heat shield structure should be provided similarly to thecase with the temperature fuse 10. Good heat insulation will be providedby covering it with a heat insulation sheet, whereby adverse effects onthe bimetal element inside will be avoided reliably.

A bimetal thermostat provided with an outer covering of heat insulatingresin excluding the parts that are heat-coupled to the rechargeablebattery shields itself from heat during the resin molding, and with sucha thermostat, no heat insulation sheet will be necessary.

Some of these heat sensitive elements with different operatingtemperatures may be used in combination according to the design.

In addition to the heat sensitive element heat-coupled to therechargeable battery 2, a pattern fuse that has an irreversible currentcutting function and stops current flow when the current exceeds apreset limit may be provided on the circuit substrate 3, so as toimprove the reliability of the battery pack with several elements havingcurrent limiting/cutting functions. In this case, too, the molten resinwill adversely affect the pattern fuse similarly to the case with thetemperature fuse 10 and PTC element, causing deterioration in variouscharacteristics of the pattern fuse as mentioned in the paragraphdescribing the problem to be resolved by the invention. Therefore, thecircuit substrate 3 should include an element that shields the patternfuse portion from heat of the molding resin. More specifically, thestructure wherein a heat shield is provided by constituent elementsexcept for the resin as set forth in claim 1, or, the structure whereina heat insulation member is provided as set forth in claim 2 may beadopted to achieve the effect of eliminating thermal effects as has beendescribed in the foregoing.

INDUSTRIAL APPLICABILITY

According to the present invention, as described above, when uniting therechargeable battery and the substrate formed with external terminalswith a gap therebetween by filling resin in the gap to form the batterypack, measures are taken so that the heat sensitive element placed inthe gap is not destroyed by the heat of the filled resin; the inventionthus provides a battery pack that has a resin-packed rigid structure.

1. A battery pack comprising: a substrate being formed with an externalterminal arranged on a sealing plate side of a rechargeable battery witha gap therebetween and united with the rechargeable battery by resinfilled in that gap; and a heat sensitive element being heat-coupled tothe rechargeable battery arranged in the gap and provided with a heatshield by constituent elements of the battery pack except for the moldedresin.
 2. A battery pack comprising: a substrate being formed with anexternal terminal arranged opposite a rechargeable battery with a gaptherebetween and united with the rechargeable battery by resin filled inthat gap; and a heat sensitive element being heat-coupled to therechargeable battery arranged in the gap and covered by a heatinsulation member.
 3. A battery pack comprising: a substrate beingformed with an external terminal arranged on a sealing plate side of arechargeable battery with a gap therebetween and united with therechargeable battery by resin filled in that gap; and a heat sensitiveelement being heat-coupled to the rechargeable battery arranged in arecess formed in the sealing plate and provided with a heat insulationmember or other constituent elements covering the recess.
 4. A batterypack comprising: a substrate being formed with an external terminalarranged on a sealing plate side of a rechargeable battery with a gaptherebetween and united with the rechargeable battery by resin filled inthat gap; and a heat sensitive element being heat-coupled to therechargeable battery arranged in the gap and formed with a heatinsulation coating layer.
 5. The battery pack according to any one ofclaims 1 to 4, wherein the heat sensitive element is a temperature fuse.6. The battery pack according to any one of claims 1 to 4, wherein theheat sensitive element is a PTC element.
 7. The battery pack accordingto any one of claims 1 to 4, wherein the heat sensitive element is abimetal thermostat.
 8. A method for manufacturing a battery packcomprising: arranging formed with an external terminal connected to arechargeable battery to the rechargeable battery with a gap therebetweenfor forming an object to be resin packed; placing the object to be resinpacked inside a die; and filling the gap with resin for uniting therechargeable battery and the substrate, wherein the die in which theobject to be resin packed and resin is filled in the gap is formed of amaterial having good heat conductivity at least in a portioncorresponding to the position where a heat sensitive element arrangedinside the gap is located.